Tone control system



Oct. 1s, 1938. P. F., G. HOLST TONE CONTROL S YSTEM Filed Dec. 2l, 19342 ShQei'S-Sheail l INVEN'TOH A A'r'rafr/VEY oct. 18, 193s.

PBH-CENT 0F' 1000 CYCLE RESPONSE PER-CENT 0F' 1000 CYCLE RESPONSE FiledDeo. 21, 1954 2 sheets-sneek 2 100 FREQUENCY IN CYCLES PER SECOND .PaulFG'. Holst ATTOR EY Patented Oct. 18, 1938- UNITED STATES TONEV CONTROLSYSTEM APoul F. G. Holst, Audubon, N. J., assignor, by mesneassignments, to Radio Corporation of America, New York, Delaware N. Y.,a corporation of Application December-21, 1934, serial No. 758,602

7 Claims.

, The present invention relates to toner control systems for radioreceiving apparatus andthe like, and has for its principal object toprovide an improved tone control` system havinga relatively sharpvariable low frequency cut-01Tv characteristic.

It is a further object of the present invention to provide an improvedtone control system providing high pass filter means for an, audiofrequency cut-oiT-characteristic.

It is also an object of the present invention to provide, in radioreceiving apparatus, an audio frequency signal circuit having. variablelow f-requency tone control means providing relatively sharp lowfrequency lcut-off characteristic and means responsive to a change inan` operating quency signal circuit having a variable low freconditionof the apparatus, such as wave band change, for changing the range ofkcontrol of said tone control means. f

It is a still further object of the present in- Vention to provide, inan audio frequency signal transmission circuit, combined toneand volumecontrol means providing variable low pass filterv means and variablehigh pass lter means,

" whereby the frequency characteristic of said system may be variedbetweenA wide limits.

It is also a further object of the present invention to provide, in anaudio frequencysignal transmission circuit, low frequency tone controlmeans comprising high pass lter elements, one of which is Variable, andhigh frequency tone control means comprising low pass filter elements,one of which is variable, in conjunction with interstage couplingmeans'andvolume control means for said signal transmission circuit.

It is also an object of the present invention to provide, in an audiofrequency signal transmission circuit, a lter network having a variableelement providing low frequency tone control means, a second lternetwork having a variable element providing high frequency tone controlmeans, and volume control means in'- terposed in said circuit betweensaid first and second named means whereby they are operable in the samecircuit.

The invention will, however, be better understood from the followingdescription when considered in connection with the accompanyingdrawings, and its scope will be pointed out in the appended claims. Inthe drawings, l

Figure 1 is a schematic circuit` diagram'of a radio receiver showing anembodiment of theinvention,

Figs. 2, 3, and 4 are fragmentary circuit dia- (Cl. Z50-20) grams of aportion of the circuit shown in 1 certain frequency-responsecharacteristics of 5 the circuits of Figs. 1 to4, inclusive.

Referring to Fig. 1, II is a radio receiver or other source of signalshaving an audio frequency transmission channel or circuit, repre-ysented by leads I3 and I5 forming the output circuit in the presentexample, of a detector tube I1 and being coupled through suitabletransfformer coupling means I9 with .-a .plurality of audio frequencyamplifier vtubes 2|. Y'I'he tubes 2|, in turn, are coupled through a`suitable ampliiier indicated at 23 with an output device such as a loudspeaker, indicated at 25. l

The audio frequency transmission circuit I3-I 5 is provided with shuntvolume control potentiometer means comprising a resistor 21 connected inshunt across the circuit and having a variable output tap 29. 'Ihevolume control means is preferably compensated by suitable shuntcircuits indicated at 3| and 33 for controlling the tone with volume,and for that reason the receiver II is preferably provided withautomatic volume control means as indicated bythe legend. Y Y

'Ihe receiver II also, is preferablyiprovided with sensitivity Vcontrolmeans indicated at 35. and in present receiver Vconstruction may-alsoembody a wave band selector means :indicated at 31 whereby the receiveris selectively adjustable for receiving signals over a plurality ofdiffering wave bands.

I'he detector anode circuit, indicated at 39, is suitably coupled to theaudio frequency transmission circuit I3-I5 through an anode couplingresistor 4I and condenser 41. Anode potential is supplied through altercomprisinga series resistor 43 and a shunt by-passvcondenser 45. Y

Interposed in the audio frequency transmission circuit, between thecoupling condenser 41 and the volume control resistor or potentiometer21, is a lter network comprising a series condenser 49 of relativelylower capacity thanrthe coupling condenser 41 and two series connectedimpedance elements arranged in shunt. across the circuit between thecoupling condenser 41 and the series condenser Y49 as indicated at 5Iand 53. The .element 5I is a resistorvof relatively high value arrangedto provide .a potentiometer between a terminal indicated at A connectedwith the transmission'circuit between the two condensers and a terminalB connected with one end of the element 53. The latter element is anaudio frequency choke coil having its opposite end connected asindicated at 55 with the lead I5 which is the low potential side of thetransmission circuit. In the present example the coupling elementscomprise the condenser 41 which may have a value of substantially .25mfd. While the series condenser 49 mayy have a Value of .025 mfd. Theresistor 5| mayv have a resistance value of about 200,000 ohms and thechoke coil 53 may have a value of `approximately 13 henries and about1500 ohms D. C. resistance.

It will be seen that the vseries connected filter elements 5I and 53 areconnected in shunt with the audio frequency signal transmission circuitacross the input side of the series condenser 49, the resistor elementbeing connected adjacent tothe high ,potential side or lead I3 and thechoke coil element `53being connected Ladjacent to the low potentialside or lead I5. The resistor 5I is provided with a movable ycontactindicated at 51, which i's connected "with the 'output side of theseries `condenser` s`49 and with 'the high potential side or lead I3jasindicated at 59.

With 'this arrangement, the'contact 51 fis -movable between the-terminals A and B vto variably short circuit 'the condenser 49 as it ismoved toward the terminal A 'and'to place 'the choke coil 53 effectivelyacross the output side of the condenser v4'9 lwhen the -contact 'ismoved toward 'and to ,the Vterminal 2B. Y

The effect of this control means on 'the transmission xcircuit 'willbeseen by reference to Figs.v 2 and 3 along with Fig. l, like parts insaid figures bearing the same reference numerals as in Fig. 1.

Fig. '2 represents the Vcondition oi -the circuit when the contact '51Vis moved to th'e position A, short-circuiting the i'condenser 4 9, asindicatedby thebridging lead "`6'Iv inFig. '2, fand placing the'resis'tor 5I Tully in "series with :the choke coil 53, therebyrendering the latter 'as well 'as the -vcondenser substantiallyineiect'ive tocontrol 'the frequency characteristic oi the ytransmissioncircuit and lgivingmaximum lo'w frequency 'transmission eiciency. Thetransmission e'iiiciency, furthermore, is indicated in Fig. 5 by thecurve A plotted between 'the 'coordinates indicated and taken with agiven 'input potential at vthe detector measured across 'the terminalsof the volume 'control pote'ntiome'ter '21.

When the conta'ct251'is 'moved to the'postion B, the circuit thenfassumes the connections indicated in Fig. 3 wherein the choke lc'oil 53is moved to the loutputside of 'the seriescondens'er 49 fdirectiyinshunt :across the :signal transmission-'circuit, and fthe series:condenserf49 is shunted bya relatively high resistance provided "by theresistance element 5I whichl is substantially Eineif ective "to'change'the leffect -of the condenser in the circuit. The result is suchthat the low frequency signals through the transmission circuit are notonly fattenua'tedby the series element 49,'but are 'furtherLattenuated'by the shunt `velement "53 which in conjunction 'with theseries condenser l49 pro- Vides ahighlpass filter, the frequencycharacteristic'of which is indicatedfbythecurve B in "Fig. 5. 'It willbe noted that a llarge percentage of the low frequency response y*of thecircuit lis'cut ofi and thatv the 'slope of the'jcurveB is relativelysharp, asis desirable. Thisis for the reason that the circuit is thenarranged substantially as .a high pass iilter in the audio frequencytransmission circuit. The 'effect oi the lter may be adjusted betweenthe limits indicated by the curves A and B by adjustment of the contact51 along the potentiometer resistor 5|.

It should be noted that in the position B shown in Fig. 3, the seriescondenser 49 is the controlling series element since it is relativelylower in capacity than the Ycoupling capacity 41 while in the positionindicated in Fig. '2 the coupling con denser 41 is the controllingseries element and its capacity determines the low frequency response ofthe system.

From the foregoing description it will be seen that the .series circuitcapacitor or condenser 49 .is short-.circuited-and a suiiicientresistance is put in series with the -inductance 53 to render its loadacross the circuit negligible, with the contact 51 at the terminal A,and that when the 'arm `51 is placed "in the position B, therelsistan'ce is placed across the condenser 49 and is suiciently high tomake the impedance of the parallel combination 5i -49 almost completelycapacitative, lwith the impedance `of the choke coil 53 `shunted acrossthe volume control resistor '21 or acrossthe audio ireq-uencytransmission circuit, thereby-forming -a high pass filter variablebetween relatively wide limits and having -a relatively sharp low`frequency cuto'if characteristic in the minimum low frequency responseposition. `On the Aoutput side oi 'the volume control means 21-29 a lowA-p'ass filter 'arrangement is provided having a variable elementproviding l'iigh'jirequency'tone control lmeans. This is `provided by a`choke coil63 in fser-ies l:wi'tli'the p'rimaryf65 Iofthe transformer I9Aand =a -shunt'lcondenser 51 connec'tedacross the secondary 69 -of thetransformer through ia variable high lresistance ".I I Additionalcapacity .may be provided `by fa 'sh-unt condenser indicated 'at T13.The arrangement is 4such that the coil isresonated Yat-'a high'frequency peak-and this may be reduced byrdecreasfing the resistance of-:the resistor 1'I to place fthe condenser 61 "in shunt with'thefsecondary. n

"Iiheihigh 'frequency response peak "is 'indicated at L "in Fig. l`6 Ionfthe 'curve '71, and is desirable in the audio lfrequency transmission7character'istic ofthe system to'compensa'te orthe attenuation yoi thehigh rrequencyfend 'of the range inthe 'radio circuits. The `iowifrequency ypeak caused bythe loud "speaker is aiso'indicated atS Y'onthe curve 11.

The four-ve T.1 represents a :condition o'f `maximum high :and lowfrequency response through the audio '-irequency transmission circuit,`with the low irequency iton'e lcontrol means 51 vadjusted fin theposition A land 'the 'resistance TI Wholly'in Icircuit 'infseries with'the condenser YB1. The effect-of reducing the'low'i-re'quency :responseby operation fof the contact 5W tothe position B is shown 'by the dashand double dot line curve 19 while the effect lupon the Joverallresponse of reducing the resistance 'o'f 'the resistor 1`I lto zero isshown 'by 'the dash Iline curve 8l. Y

The effect of reducing both 'the high and low .frequency controls forminimum low Aand high frequency response `Iis indicated by the dash anddot linecurve 83. l*It willthus be seen that complete control of theaudio frequencycharacteristic Eoi the "transmission system may 'belobtained 'by 'the two iilter'networks 'interposed in the circuit'onopposite'sides-oifthe volume control means provides a low pass filterwith a variable :high frequency cut-off, characteristicon the outputside of the volume :control means for .the 'audio' frequencytransmission circuit. Signals ofsubstantially constant average amplitudeare supplied to the detector from the receiver having automatic volumekcontrol means andthe volume and frequency characteristic thereof may beadjusted by the low and high frequency tone control means and theinterposed volumecontrol means.

In connection with ajmulti-wave receivenit has been found 'that it isdesirable to limit the control range of the low frequency tone controlmeans or lter network when receiving signals in certain ofthe higherfrequency bands; It has further been found that the range of 'lowfrequency tone control may be reduced by maintaining the high passfilter in the circuit as a permanent part thereof and permittingonly theseries condenser element to be varied.-- This is provided in the circuitof the present example by providing suitable means such as a switch Y93for, connecting the contact 51 with the terminal 13r of the'seriesresistor 5| whereby the choke coil 253 is permanently connectedacrossthe `audio frequency transmission circuit onthe output side of theseries condenser 49. l Adjustment of the contact 51 along the resistor5| the relative series effect in the circuit of the series condenser 49with respect tothe coupling condenser 41, the latter being eifectivetocontrol the circuit when the resistor 5| is substantiallyv out ofcircuit, the contact 51 being in the position A and the choke coil 53remainingin shunt,

across the volume control resistor 21 or across theaudio frequencytransmission circuit on the output side of the series condenser 49.

It will be noted that with the contact 51 in the position B and with theswitch 93 closed, the same condition exists in Fig. 4 as exists in Fig.3 for a minimum low frequency response, and the system is adjusted tooperate in accordance with the curve B of Fig. 5, or the curve 19 ofFig. 6, measurements being taken at the loud speaker for the lattercurve instead of at the volume control terminals. However, as theresistor 5| is short-circuited gradually across the condenser 49 the lowfrequency response is increased because of a reduction in the seriesimpedance in the circuit presented by the condenser 49 and the responsecharacteristic of the system reached that indicated by the curve C ofFig. 5 showing that the low frequency tone control has been reduced fromthe limits A-B to the limits C B.l In other words, the low frequencyresponse of the system is reduced to a new and higher low frequencylimit, and this has been found to be desirable to prevent howl, that is,acoustical feedback, and low frequency cabinet resonance in highfrequency all-wave receivers. The acoustical feedback may result, as isWell known, through vibration of the various parts of the receiver bysounds from the loud speaker. Other disturbances and beat notes at lowfrequencies are also reduced by this means.

The effect upon the overall response of the receiver of the adjustment Cof Fig. 5 is shown in Fig. 6 by the curve |93. It will be noted thatwhile the loud speaker response peak is predominant, it is materiallyreduced to a relatively low level, as indicated at S', in comparison tothe high frequency response peak L.

In order that the low audio frequency response vthen serves to varyindicated -by the dottedline '95, with the switch 93to 'be operabletherewith or thereby.

kIn the present example, the switch 'is providedwith five contacts 91corresponding to ve different vwave. bands, the wave bands'over whichcompensation vfor Vthe low frequency response is desired being connectedin circuit by the arm 99 of the switch, with the choke coil and contact51 through leads -|.0|. The switch 93 thus provides selector means forconnecting lthe contact 51 with terminal B, thereby changing the lowfrequency cut-off point of the high pass filter and vlimiting the low`frequency tone control range for certain of the receivedwave bands. Byconnecting the switch with the wave band-selector, the low frequencytone control range is automatically -ad- J'usted with the wave band.

In the foregoing description it will be seen-that .in an audio frequencytransmission system a low range may be .reduced with? increase kkin thefre-- adapted-to a transmission circuit having therein a,shunt1vo1umecontrol means, the one filter being `connected on one side thereof andthe other on theopposite side of said volume control means whereby allthree controls are operable in the same circuit independently of each`other.

In the present example a series coupling conn denser of relativelylargevalue is followed by a' series condenser of relativelylower-valueina variable high pass filter arrangement comprising a resistor and achoke coil vin series across the transmission circuit on'the input sideof the lcondenser between the high potential and the low potential sidesof the circuit. The contact on the resistor is connected with the outputside of the series condenser, and the high frequency tone control meanscomprises a series choke vcoil in the primary of an audio frequencycoupling transformer lto reduce the high frequency response peak tol avalue within the desired audio frequency range and a shunt condenserprovided with series variable control r means across the transformersecondary. i

While my invention has been illustrated and described in connectionsignal circuit for a radio receiver, it is not limited thereto but maybe applied to any audio frequency signal circuit requiring either orboth, high and low frequency tone control, in conjunction with the loudspeaker, and limitation of the low frequency tone control range forcertain conditions of operation. To this end the control means 93 may beactuated manually or by any other suitable means.

I claim as my invention:

1. In a multi-wave radio receiver, the combination with an audiofrequency signal transmission circuit, of a condenser in series and achoke coil in shunt with said circuit providing a high pass filter meanstherein, and variable control means with an audio frequencyY connectedwith said condenser and choke 'coil for gradually rendering saidcondenser effective named meansfand saidvlimitingmeansforsimultaneousoperation therewith. Y p H2. 'Ihe `combination With 'a radioreceiver, of signal waveband selector means, variable low frequencytonecontrol meanshaving a predeterminedtone control range of variation forone Wave band, and means simultaneously operable with and bysaid Waveband selector means vfor limiting the effective frequency range of.control provided by variation of said tone control means for anotherWave band.

3. In a radio receiver, the 'combination with signal Wave band changingmeans, of manually variable electrical circuit means'for varying the lowfrequency response lcharacteristic of said receiver within apredetermined frequency range for one Wave band, and means connectedwith and operable by said wave band changing means for limiting theeffective frequency range of control provided by variation of saidsecond named means for another wave band.

4. In a radio receiver, the combination with Wave band changing means,of means for varying the low frequency response characteristic ofsaid'receiver, said means lcomprising an audio frequency transmissioncircuit, of a condenser in series and 'a choke coilconnected in shuntwith said circuit providing a high pass filter means therein, variablecontrol means connectedwith said condenser and choke coil for graduallyren'- dering said condenser effective in said circuit as a seriesimpedance element and said choke coil as a shunt impedance element onthe'signal output side of said condenser, and -means connected withVand' operable by-said Wave band changing means 'for limiting the rangeof variation of said second named means.

- 5. The combination with a receiver adjustable to receive signals overa plurality of frequency bands, "of means for varying the low audiofrequency Ytone'charac'teristic of said receiver, and means for limitingthe low yfrequency end of said variation range when said receiver isadjusted to respond to signals in certain of said frequency bands. f

6. 'I'he combination with a receiver adjustable to receive signals overa plurality of frequency bands, of means for varying the low audiofrequency tone characteristic of said receiver, means for limiting thelow frequency end of said variation range when said receiver is adjustedto respond to certain of said frequency bands, separate means formanually controlling the volume of said receiver associated in circuitwith said first named means, and separate means for controlling the highfrequency tone characteristic of said receiver. v l

'7. The combination with a receiver adjustable to receive signals 'overa plurality of frequency bands, of means for varying the low audiofrequency tone "characteristic of said receiver, and meansforlimitingthe low frequency end of said variation range when said receiver isadjusted to respondto certain of said frequency bands,

said first named means including an audio frequency circuit, an audiofrequency choke coil connected in shunt relation to said circuit, aseries capacitor in said 'circuit and a variable resistance device forjointly controlling the effect of said f' capacitor and choke coil insaid circuit, and said last named means comprising a frequency bandchanging device and switch contacts connected therewith for connectingsaid ,audio frequency choke coil across said audio frequency circuitindependently of the operation of said Variable resistance device.

" Y POUL F. G. HOLS'I.`

